Apache Tomcat is required to create a java model. See here where to download it from and how to install it.
Having Apache Tomcat 5.5 installed on your machine (*), just create a new KB for Java Environment and then build any object.
You only need to set the database information properties.
And GeneXus will automatically determine for you the rest of the information needed!
You don't need to worry about remembering these paths nor even type them.
Thus, from now on someone who isn't familiar with Java (or doesn't know what these properties mean necessarily!) will be able to easily create and run a Java Application in minutes.
GeneXus will automatically create a Web Application within the servlets engine and set the properties to it, also will set the classpath with all the classes and drivers needed (JAR files), and finally find where your Java Virtual Machine compiler and interpreter are installed.
Now, just startup your tomcat and run F5 in GeneXus.
So, to create a new Java Model in GeneXus X it's as simple as 1, 2, GO!
If you modify the Servlet Directory model property the web application automatic configuration is not done, you must complete the application configuration manually; generally this means:
configure the web.xml and context.xml files in the WEB-INF folder.
copy all the libraries to the \WEB-INF\lib\ folder.
(*) This functionality is not available with versions prior to Apache Tomcat 5.5. Note for JDK 1.5.0_11 version users:
In this case the java compiler path that Genexus takes will not be the correct one because of this bug of the jdk setup: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6520670 (this link shows the bug report and how to fix the registry problem)